I tried taking the front facing walking animations of the guards, and making their attack frames in the walking frames (so they're attacking while moving forward). It didn't go well, but I think someone like doomjedi or Ringman would be able to pull it off.

My issue was getting the gun to look more fluid with the movement, instead of appearing stiff.

For the attack frames to look consistent with the front-facing frames, the guard has to stand upright, open his legs, and stand with his legs in an upside-down "V" shape. You'll have to achieve this with the 7 frames you're trying to create. The top half of the walking/running images will still be useful, but you'll probably have to do most of the bottom half from scratch.